Tubular reactors are often used for carrying out reactions involving fluid components, such as reforming hydrocarbon fuel. Hydrocarbon fuel reformers such as diesel fuel reformers can be used in various applications, including providing a hydrogen and carbon monoxide reformate that can be used as fuel for a solid oxide fuel cell. These reactors typically include a catalyst monolith disposed inside a tube, through which fuel flows. The catalyst catalyzes a reaction of the hydrocarbon fuel to convert it into hydrogen and carbon monoxide.
One important requirement for reactors such as hydrocarbon fuel reformers is to provide adequate heat transfer into the catalyst to maintain endothermic reaction conditions. Multiple techniques and concepts may be utilized to provide the required thermal conditions. As an example, reducing the diameter of a catalyst while maintaining its length both reduces the catalyst mass and therefore its heat capacity, and also reduces the heat transfer path. This approach, however, requires the use of multiple catalyst segments to maintain total catalyst volume and the resultant space velocity at a given flow rate. When such a strategy is utilized, the system must therefore be engineered to create uniform space velocities among all of the catalyst segments. Another technique to promote heat transfer is to increase the surface area separating the two fluids across which the heat transfer occurs. In practice, this is typically accomplished by incorporating heat transfer fins that are intimately attached to the catalyst tube(s) that project into the hot fluid flow path.
In order to exercise a high degree of control over the respective orientations of the tubes in a multi-tube reactor, a typical manufacturing approach is illustrated in FIGS. 1-4. The first step in this approach, as shown in FIG. 1, is the provision of a housing 12 having a number of fins or foils 14 disposed therein. Next, as shown in FIG. 2, a series of holes 16 are formed in the fins or foils 14 in a configuration to provide the desired distribution of fluid velocity and thermal kinetics. These holes may be formed by any of a number of known techniques, such as electronic discharge machining (EDM), laser machining, or mechanical boring. Then, as shown in FIG. 3, tubes 18 having catalyst monoliths 20 disposed therein are inserted into each of the holes 16, and fixed in place with adhesive or metal brazing.
This prior art process, however, is subject to several problems. The forming of the holes 16 through the relatively delicate (typically about 0.04 mm thick) fins or foils 14 using conventional techniques such as EDM can be a time-consuming and expensive process. Additionally, insertion of the tubes 18 into the holes 16 subjects the foil along the periphery of the hole to damage and/or distortion because of the fine gauge of the foil. This can lead to small gaps 22 between the outside edge of the tube 18 and the foil 14, as shown in FIG. 4 (gaps may be exaggerated for purposes of illustration), which reduces the effectiveness of the heat transfer between the warmer fluid in the area of the foil matrix 14 and the colder fluid within the volume of the catalyst monolith 20.
Accordingly, there is a need for a more effective multi-tube reactor design and manufacturing method that is less susceptible to the above-described problems.